Robert Pondiscio of Core Knowledge points to a new study showing that, despite adults' best intentions, kids get lied to a lot. While parents specialize in fabricating false threats in order to influence behavior--the study's lead researcher himself admits to telling his son there's an eject button in his car--teachers tend go in for the "confidence-boosting lie." The study apparently doesn't examine the impact of all this fibbing on kids, but Pondiscio speculates about the effects of his own elementary school teachers' practice (prescribed by the Teacher's College Writer's Workshop) of arbitrarily complimenting all student work:
The intended effect obviously was to boost confidence and inspire additional effort. The danger (equally obvious) was that students might overestimate their ability, slack off, and be set up for disappointment later on.
It's a difficult balance, plainly. But then, it's worth noting that Pondiscio himself pretty clearly turned out to be a very good writer.